Gas turbine engines are started using air turbine starters which receive pressurized air from, for example, a separate air compressor or from the auxiliary power unit of an aircraft. Air flow to the starter is generally controlled by a starter valve which acts as an on/off valve, restricting flow to the starter. In prior art systems, the position of the starter valve has been measured using, for example, electrical switches connected to the actuator mechanism which controls the position of the valve plate. However, using switches to determine the status of a valve provides limited information about failures. Further, electrical switches actuated mechanically are difficult to test without removing the switch and testing it separately because such systems generally cannot distinguish between switch failures and valve failures.
It would, therefore be advantageous to design a valve position sensing system which is reliable and testable. Further, it would be advantageous to design a valve position sensor which provides information on the air pressure at the input to the starter.